"00" followed by a "0", or a "0" followed by a "00". However, this is a limitation on the notation for writing strings, not on their underlying definitions. Like any finite set, {00,0} can be used as an alphabet, whose strings can be written unambiguously in a different notational convention with commas separating their elements: 0,00 != 0,0,0 != 00,0.

Notation

By definition, the alphabet of a formal language over is the set , which can be any non-empty set of symbols from which

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